Memory circuit of an electric shutter

ABSTRACT

An exposure control arrangement for a camera having an objective lens and a shutter moveable between closed and open positions is disclosed. A light intensity to voltage conversion means is positioned behind the objective lens for converting essentially each value of the intensity of the light passing through the objective lens during use of the camera to a voltage having a value essentially linearly proportional to a logarithm of the value of said intensity, and a capacitor memory means is selectively coupled to the conversion means for storing this voltage. Switch means are provided for selectively coupling the capacitor memory means to the conversion means during intervals when light passing through the objective lens is incident on the conversion means and for disconnecting the capacitor memory means from the conversion means when the light passing through the objective lens is not incident on the conversion means. The camera shutter is actuated by a control means which is coupled to the capacitor memory means and which controls the open time of the shutter in accordance with the voltage stored in the capacitor memory means.

United States Patent Yamada et al.

[54] MEMORY CIRCUIT OF AN ELECTRIC SHUTTER [72] Inventors: Takeo Yamada,Tokyo; Shigeo Ono,

Yokohama-shi, both of Japan [73] Assignee: Nippon Kogaku K.K., Tokyo,Japan [22] Filed: Jan. 2, 1968 21 Appl. No.: 695,200

[52] US. Cl ..95/l CT, 95/53 EB [51] Int. Cl ......G0lj /30, G03b 7/08[58] Field of Search ..95/53, 250/214 [56] References Cited UNITEDSTATES PATENTS 3,533,348 10/1970 Yanagi ..95/l0 C 3,503,314 3/1970Tanabe ..95/l0 C 3,474,713 10/1969 Mori et al. ..95/l0 C 3,486,43412/1969 Suzuki et al ..95/l0 C X 3,179,808 4/1965 Grey et al. ..95/53 X3,504,603 4/1970 Brzonkala ..95/10 C 3,429,242 2/1969 Yoshida et al...95/l0 C 3,205,767 9/1965 Weber ..95/l0 3,324,779 6/1967 Nobusawa..95/l0 X 3,336,850 8/1967 Otani ..95/10 3,368,468 2/1968 Rentschler..95/l0 3,433,140 3/1969 Wick ..95/l0 3,437,027 4/1969 Straub ..95/53 X3,693,518 Sept. 26, 1972 Attorney-Anton J. Wille [5 7 ABSTRACT Anexposure control arrangement for a camera having an objective lens and ashutter moveable between closed and open positions is disclosed. A lightintensity to voltage conversion means is positioned behind the objectivelens for converting essentially each value of the intensity of the lightpassing through the objective lens during use of the camera to a voltagehaving a value essentially linearly proportional to a logarithm of thevalue of said intensity, and a capacitor memory means is selectivelycoupled to the conversion means for storing this voltage. Switch meansare provided for selectively coupling the capacitor memory means to theconversion means during intervals when light passing through theobjective lens is incident on the conversion means and for disconnectingthe capacitor memory means from the conversion means when the lightpassing through the objective lens is not incident on the conversionmeans. The camera shutter is actuated by a control means which iscoupled to the capacitor memory means and which controls the open timeof the shutter in accordance with the voltage stored in the capacitormemory means.

13 Claims, 6 Drawing Figures TIME CONT- swlT ROL CIRCUIT c| 0 7 a 3 bTIME CONT- SWITCH J f c ROL CIRCUIT CIRCUIT F 10 4 L PIITENTEDSEMB I912SHEET 1 [IF 2 IFIG.I

SWITCH CIRCUIT ROL CIRCUIT FIG.2

SWITCH CIRCUIT TIME CONT- ROL CIRCUIT FIG.3

SWITCH CIRCUIT TIME CONT- ROL CIRCUIT PATENTEDSEP26 I972 SHEET 2 BF 2 R77 1 0 g TIME CONT- SWITCH g 10 C ROL CIRCUIT CIRCUIT 4 T s e FIG. 5

TIME CONT- SWITCH ROL CIRCUIT CIRCUIT Fl G. 6

TIME CONT ROL CIRCUIT SWlTCH CIRCUIT MEMORY CIRCUIT OF AN ELECTRICSHUTTER In electronic exposure controlled single lens reflex cameras, ithas become the practice to provide the light intensity sensing elementwithin the camera body to provide increased flexibility of the camera inan interchangeable lens system. When, for example, the light sensingelement is provided on the back surface of the pentaprism, the movementof the mirror out of the lens-film path prevents light from falling onthe light sensing element. This, then, requires that the light intensitybe somehow memorized before the inovement of the mirror.

ln cameras utilizing typical exposure meters, wherein a voltage source,resistor, and photoconductor (i.e., a resistor whose resistance varieswith light intensity) are series connected, it has been proposed that acapacitor be used to store or memorize the voltage drop across theseries resistor.

A problem develops, however, when one attempts to memorize the range ofvoltages produced by the series resistor. The resistance R of thephotoconductor may be represented as a function of brightness B asfollows:

where a is a constant and 'y is a constant determined by the propertiesof the photoconductor. Thus, for the 17 stages of measuring range usedin the EV (exposure value) system, if y is taken as equal to unity, themaximum value of R becomes 2 or approximately 1.3 X times the minimumvalue. Trying to memorize voltages varying over such a range isobviously difficult and entails very small changes in output for changesin light intensity.

In view of the foregoing, it is therefore an object of the presentinvention to provide an exposure measuring system wherein the abovedifficulties are largely eliminated.

The foregoing object and other advantages are achieved in the presentinvention wherein there is provided a linearizing circuit for use with amemory circuit. The linearizing network comprises a resistance networkor semiconductor device, such as a diode, which transforms theexponential response into a linear one. Stated another way, the networkconverts the light intensity of the scene to be photographed into avoltage having a value essentially linear proportional to a logarithm ofthe value of said intensity. An exposure meter in accordance with thepresent invention would thus comprise a photoconductor in series withthe linearizing means and coupled to a source of operating voltage. Thememory element, typically a capacitor, is connected in parallel with thelinearizing means. Other features of the present invention include theprovision of a means for disconnecting the memory element duringoperation of the shutter and an indicator, connected in parallel withthe memory element, mechanically coupled to a light intensity controlmember so that movement of the indicator controls the intensity of lightincident upon the photoconductor.

The various features and advantages of the present invention may be morefully understood by considering the following detailed description inconjunction with the accompanying drawings, in which;

FIG. 1 shows an illustrative embodiment of a circuit of the presentinvention where a resistor is used;

FIG. 2 and FIG. 3 show, respectively, modified embodiments of FIG. 1;

FIG. 4 shows another embodiment using a diode;

FIG. 5 shows another embodiment in which a transistor is used in placeof the diode in FIG. 4; and

FIG. 6 shows a modification of FIG. 4.

Referring to FIG. 1, there is shown photoconductive elements R and R,whose resistivities are a function of the brightness of the externalfield to be measured. R R and R are fixed resistances. R, and R act asproportioning devices and the resistance R. can sometimes be omitted,depending upon the amount of current through R,. Element 1 is a sourceof operating potential and has series connected thereacrossphotoconductors R and R and fixed resistances R and R Fixed resistance Rconverts into voltage variations the current variations produced by thechanges in resistance of photoconductors R and R and has connected inparallel therewith indicator means 2 and series connected switch 3 andmemory element 4, which is shown by way of example as comprising acapacitor. As shown in FIG. I, switch 3 comprises three terminals in asingle pole, double throw configuration. Terminal a may be considered tobe the memory side of switch 3 and connects capacitor 4 to the voltageproducing resistance R,,. While it is so connected, capacitor 4 storesthe voltage produced by R, which is portional to a logarithm of theamount of light incident upon photoconductors R, and R When the shutter,which is mechanically coupled to switch 3 is activated, switch 3 thenconnects memory capacitor 4 to what may be called the read-out side ofswitch 3, terminal b. In this position, the voltage stored on memorycapacitor 4 is presented to time control circuit 5. Time control circuit5 controls the exposure time by means of a signal derived from thevoltage accumulated on memory capacitor 4 and transforms thearithmetical or linear function of said signal into a geometrical orexponential function of exposure time. Time control circuit 5 has itsoutput connected to a switch circuit 6, which, in turn, controls theshutter mechanism, thereby determining the exposure time. Switch circuit6, in response to the exponential time control signal, energizes orde-energizes electromagnet 7 which may, for example, hold the rearscreen of a focal plane shutter whereby the rear screen is enabled torun, closing the shutter mechanism.

Thus, it can be seen that by the present invention the extremely widerange of values normally presented by a photoconductor exposure meterhas been reduced by linearizing the response of the meter. Thislinearized function is then readily stored on a capacitor memory whichthen can be switched between a memorizing mode and a read-out mode inaccordance with the operation of the shutter mechanism. In this manner,any discontinuities induced by the mirror interfering with the lightincident upon photoconductors R and R is obviated. Indicator 2 merelyserves to indicate to the user the shutter speed determined by themeasuring circuit.

When the resistivities of photoconductors R and R and resistances R Rand R are properly selected, the voltage drop across resistance R, willbe changed from an exponential function to a linear function, relativeto the change in external brightness. Thus, the range of values thatmust be accurately memorized by capacitor 4 is greatly narrowed.

In FIG. 2 there is illustrated another embodiment of the presentinvention wherein the time control circuit is continuously connected tomemory element 4 and, further, wherein resistance R is a potentiometer.These two changes may be made independently, that is, one is notnecessary with the other. By utilizing a potentiometer for resistance Rthe sensitivity of the over-all system may be modified and a fixedproportion of the linear output voltage may be obtained.

FIG. 3 illustrates another embodiment of the present invention whereinan emitter follower stage is interposed between resistor R and thememory element capacitor. The emitter follower stage comprisestransistor 8 having its base connected to resistance R,,, its collectorconnected directly to a source of operating potential and its emitterconnected to output potentiometer R Output potentiometer R functions inthe same manner as potentiometer R in FIG. 2. Transistor 8 thus acts asa greatly reduced source impedance and enables one to obtain a quickerresponse by the memory element.

Voltage source 9, which is used in powering the emitter follower stage,may be omitted by restricting the measuring range or by replacingtransistor 8, shown in the drawing as bi-polar, with a field effecttransistor. Due to the isolation provided by transistor 8, theresistivity of potentiometer R can be selected independently of theresistivities of photoconductors R and R Thus, if the resistivity ofpotentiometer R is relatively small, the change in bias level caused bythe addition of indicator 2 can be virtually ignored, provided indicator2 has a relatively large internal resistance. 7 FIG. 4 illustratesanother embodiment of the present invention wherein the response of thediode is used to convert the geometric or exponential response of thephotoconductor into an arithmetical or linear response. Specifically inFIG. 4 photoconductor R is series connected with diode 10 across asource of operating potential 1. The voltage drop across diode 10 isstored in the manner described in connection with FIG. 1. By utilizing adiode as shown in FIG. 4, an exponential-tolinear function converter isreadily obtained by utilizing the square Law of response of the diode.

FIG. 5 illustrates another embodiment of the present invention in whicha transistor having its base and collector electrodes connected togetheris used to perform the same function as described above in connectionwith diode 10, as illustrated in FIG. 4.

FIG. 6 illustrated another embodiment of the present invention whereinthe diode converter as utilized in FIG. 4 has added thereto an emitterfollower circuit as utilized and described in connection with FIG. 3.

Also illustrated in FIGS. 1, 3, and 6 is an optical wedge 12 of thevariable density type mechanically coupled to indicator 2. This couplingbetween indicator 2 and wedge 12 provides an electro-mechanical feedbacksystem whereby non-linearities in the specific components utilized maybe compensated.

Thus, it can be seen that the present invention provides a means wherebythe exponential variations in external brightness may be readilyconverted to a voltage signal that is a linear function of thebrightness and memorized. In this manner, variations in externalbrightness over a wide range may be readily stored within the exposuremeter. Further, the sensitivity of 6 the exposure meter in accordancewith the present invention may be readily adjusted by dividing thelinear of output voltage by a fixed amount and memorizing the quotient.Further, by providing an optical wedge between the light source and thephotoconductors, variations in the system may be further compensated.

Having thus described the invention, it will be apparent to those ofskill in the art that many modifications may be made within the spiritand scope of the present invention.

What is claimed is:

1. In a camera having an objective lens and a shutter moveable betweenclosed and open positions, an exposure control arrangement comprising:

light intensity to electric signal conversion means positioned behindsaid objective lens for converting essentially each value of theintensity of the light passing through said objective lens during use ofsaid camera to a corresponding electric signal having a valueessentially linearly proportional to a logarithm of said value of lightintensity;

memory means for storing said electrical signal;

switch means for coupling said memory means to said conversion meansduring intervals when the light passing through said objective lens isincident on said conversion means and for disconnecting said memorymeans from said conversion means when light passing through saidobjective lens is not incident on said conversion means; and

control means coupled to said memory means to control the open time ofsaid shutter in accordance with the electrical signal stored in saidmemory means.

2. In a camera, an exposure control arrangement as in claim 1, whereinsaid memory means includes a capacitor and said conversion meansincludes means producing a voltage essentially linearly proportional toa logarithm of the value of the intensity of the light passing throughsaid objective lens.

3. In a camera, an exposure control arrangement as in claim 2, whereinsaid conversion means includes photoconductor means responsive to thelight passing through said objective lens and diode means seriesconnected to said photoconductor means, said series connectedphotoconductor means and diode means being connected across a source ofoperating potential.

4. In a camera, an exposure control arrangement according to claim 3,wherein said diode means includes a transistor having base, emitter andcollector electrodes, said base and collector electrodes being connectedtogether.

5. In a camera, an exposure control arrangement according to claim 3,wherein said conversion means includes first and second series connectedphotoconductor means, said first and second photoconductor means beingarranged to receive said light passing through said objective lens,first and second series connected resistance elements connected inparallel with said second photoconductor means, and a third resistanceelement connected to the junction of said series connected resistanceelements.

6. In a camera having an objective lens and a shutter moveable betweenclosed and open positions, an exposure control arrangement comprising:

light responsive means for producing an output current related to theintensity of the light passing through said objective lens during use ofsaid camera;

conversion means coupled to said light responsive means for producing avoltage which is essentially linearly proportional to a logarithm of thevalue of the intensity of light incident on said light respons1ve means;

capacitor memory means for storing said voltage;

switch means for coupling said capacitor memory means to said conversionmeans during intervals when light passing through said objective lens isincident on said light responsive means and for disconnecting saidmemory means from said conversion means when light passing through saidobjective lens is not incident on said light responsive means; and

control means coupled to said capacitor memory means to control the opentime of said shutter in accordance with the stored voltage in saidcapacitor memory means.

7. In a camera having an objective lens and a shutter moveable betweenclosed and open positions, an exposure control arrangement comprising:

photoconductor means for producing an output current related to theintensity of the light passing through said objective lens during use ofsaid camera;

a transistor for producing a voltage which is essentially linearlyproportional to a logarithm of the value of the intensity of lightincident on said photoconductor means, said transistor having base,emitter and collector electrodes, said base and collector electrodesbeing connected together;

means connecting said photoconductor means and said transistor in seriesconnection across a source of operating potential;

capacitor memory means for storing said voltage;

switch means for coupling said capacitor memory means to said transistorduring intervals when light passing through said objective lens isincident on said photoconductor means and for disconnecting saidcapacitor memory means from said conversion means when light passingthrough said objective lens is incident on said photoconductor means;and

control means coupled to said capacitor memory means for controlling theopen time of said shutter in accordance with the stored voltage in saidcapacitor memory means.

8. In a camera having an objective lens and a shutter moveable betweenclosed and open positions, an exposure control arrangement comprising:

light intensity to voltage conversion means for converting essentiallyeach value of the intensity of the light passing through said objectivelens during use of said camera to a corresponding voltage which isessentially linearly proportional to a logarithm of the value of saidintensity, said conversion means including a first photoconductor, asecond photoconductor series connected to said first photoconductor,said first and second photoconductors being arranged to receive saidlight passing through sad objective lens, first and second seriesconnected resistance elements connected in parallel with said secondphotoconductor, and a third resistance element connected to the junctionof said series connected resistance elements;

capacitor memory means for storing said voltage;

switch means for coupling said capacitor memory means to said thirdresistor during intervals when light passing through said objective lensis incident on said first and second photoconductors and fordisconnecting said memory means from said third resistor when lightpassing said objective lens is not incident on said first and secondphotoconductors; and

control means coupled to said capacitor memory means to control the opentime of said shutter in accordance with the stored voltage in saidcapacitor memory means.

9. In a camera having an objective lens and a shutter moveable betweenclosed and open positions, an exposure control arrangement comprising:

light intensity to voltage conversion means for converting essentiallyeach value of the intensity of the light passing through said objectivelens during use of said camera to a corresponding voltage which isessentially linearly proportional to a logarithm of the value of saidintensity, said conversion means including a first photoconductor, asecond photoconductor series connected to said first photoconductor,said first and second photoconductors being arranged to receive saidlight passing through said objective lens, first and second seriesconnected resistance elements connected in parallel with said secondphotoconductor, and a potentiometer connected to the junction of saidseries connected resistance elements;

capacitor memory means for storing said voltage;

switch means for coupling said capacitor memory means to saidpotentiometer during intervals when light passing through said objectivelens is incident on said first and second photoconductors and fordisconnecting said capacitor memory means from said potentiometer whenlight passing through said objective lens is not incident on said firstand second photoconductors; and

control means coupled to said capacitor memory means to control the opentime of said shutter in accordance with the stored voltage on saidcapacitor memory means. 10. In a camera having an objective lens and ashutter moveable between closed and open positions, an exposure controlarrangement comprising:

light intensity to voltage conversion means for converting essentiallyeach value of the intensity of the light passing through said objectivelens during use of said camera to a corresponding voltage which isessentially linearly proportional to a logarithm of the value of saidintensity, said conversion means including a first photoconductor, asecond photoconductor series connected to said first photoconductor,said first and second photoconductors being arranged to receive saidlight passing through said objective lens, first and second seriesconnected resistance elements connected in parallel with said secondphotoconductor, and a third resistance element connected to the junctionof said series connected resistance elements;

amplifying circuit means connected to said junction for providing anoutput voltage proportional to said voltage,

capacitor memory means for storing said output voltage;

switch means for coupling said capacitor memory means to said amplifyingmeans during intervals when light passing through said objective lens isincident on said first and second photoconductors and for disconnectingsaid capacitor memory means from said amplifying means when the lightpassing through said objective lens is not incident on said first andsecond photoconductors; and

control means coupled to said capacitor memory means to control the opentime of said shutter in accordance with the stored voltage in saidcapacitor memory means.

11. In a camera having an objective lens and a shutter moveable betweenclosed and open positions, an exposure control arrangement comprising:

a photoconductor for producing an output current related to theintensity of the light passing through said objective lens during use ofsaid camera;

a diode series connected with said photoconductor for producing avoltage which is essentially linearly proportional to a logarithm of thevalue of the intensity of the light incident on said photoconductor,said series connected diode and photoconductor being connected across asource of operating potential;

capacitor memory means selectively coupled to the junction of saidphotoconductor and said diode for storing at least a portion of saidvoltage; and

control means for controlling the open time of said shutter inaccordance with the stored voltage in said capacitor memory means.

12. In a camera, an exposure control arrangement as set forth in claim11 further comprising:

an amplifying stage coupling said junction to said capacitor memorymeans, said amplifying stage being in the configuration of an emitterfollower.

13. In a camera, an exposure control arrangement as set forth in claim12, wherein said amplifying stage comprises:

a transistor having a control electrode and a potentiometer, having atap, series connected across a source of operating potential, saidcontrol electrode of said transistor being coupled to said junc tion andthe tap of said potentiometer being connected to said capacitor memorymeans.

1. In a camera having an objective lens and a shutter moveable betweenclosed and open positions, an exposure control arrangement comprising:light intensity to electric signal conversion means positioned behindsaid objective lens for converting essentially each value of theintensity of the light passing through said objective lens during use ofsaid camera to a corresponding electric signal having a valueessentially linearly proportional to a logarithm of said value of lightintensity; memory means for storing said electrical signal; switch meansfor coupling said memory means to said conversion means during intervalswhen the light passing through said objective lens is incident on saidconversion means and for disconnecting said memory means from saidconversion means when light passing through said objective lens is notincident on said conversion means; and control means coupled to saidmemory means to control the open time of said shutter in accordance withthe electrical signal stored in said memory means.
 2. In a camera, anexposure control arrangement as in claim 1, wherein said memory meansincludes a capacitor and said conversion means includes means producinga voltage essentially linearly proportional to a logarithm of the valueof the intensity of the light passing through said objective lens.
 3. Ina camera, an exposure control arrangement as in claim 2, wherein saidconversion means includes photoconductor means responsive to the lightpassing through said objective lens and diode means series connected tosaid photoconductor means, said series connected photoconductor meansand diode means being connected across a source of operating potential.4. In a camera, an exposure control arrangement according to claim 3,wherein said diode means includes a transistor having base, emitter andcollector electrodes, said base and collector electrodes being connectedtogether.
 5. In a camera, an exposure control arrangement according toclaim 3, wherein said conversion means includes first and second seriesconnected photoconductor means, said first and second photoconductormeans being arranged to receive said light passing through saidobjective lens, first and second series connected resistance elementsconnected in parallel with said second photoconductor means, and a thirdresistance element connected to the junction of said series connectedresistance elements.
 6. In a camera having an objective lens and ashutter moveable between closed and open positions, an exposure controlarrangement comprising: light responsive means for producing an outputcurrent related to the intensity of the light passing through saidobjective lens during Use of said camera; conversion means coupled tosaid light responsive means for producing a voltage which is essentiallylinearly proportional to a logarithm of the value of the intensity oflight incident on said light responsive means; capacitor memory meansfor storing said voltage; switch means for coupling said capacitormemory means to said conversion means during intervals when lightpassing through said objective lens is incident on said light responsivemeans and for disconnecting said memory means from said conversion meanswhen light passing through said objective lens is not incident on saidlight responsive means; and control means coupled to said capacitormemory means to control the open time of said shutter in accordance withthe stored voltage in said capacitor memory means.
 7. In a camera havingan objective lens and a shutter moveable between closed and openpositions, an exposure control arrangement comprising: photoconductormeans for producing an output current related to the intensity of thelight passing through said objective lens during use of said camera; atransistor for producing a voltage which is essentially linearlyproportional to a logarithm of the value of the intensity of lightincident on said photoconductor means, said transistor having base,emitter and collector electrodes, said base and collector electrodesbeing connected together; means connecting said photoconductor means andsaid transistor in series connection across a source of operatingpotential; capacitor memory means for storing said voltage; switch meansfor coupling said capacitor memory means to said transistor duringintervals when light passing through said objective lens is incident onsaid photoconductor means and for disconnecting said capacitor memorymeans from said conversion means when light passing through saidobjective lens is incident on said photoconductor means; and controlmeans coupled to said capacitor memory means for controlling the opentime of said shutter in accordance with the stored voltage in saidcapacitor memory means.
 8. In a camera having an objective lens and ashutter moveable between closed and open positions, an exposure controlarrangement comprising: light intensity to voltage conversion means forconverting essentially each value of the intensity of the light passingthrough said objective lens during use of said camera to a correspondingvoltage which is essentially linearly proportional to a logarithm of thevalue of said intensity, said conversion means including a firstphotoconductor, a second photoconductor series connected to said firstphotoconductor, said first and second photoconductors being arranged toreceive said light passing through sad objective lens, first and secondseries connected resistance elements connected in parallel with saidsecond photoconductor, and a third resistance element connected to thejunction of said series connected resistance elements; capacitor memorymeans for storing said voltage; switch means for coupling said capacitormemory means to said third resistor during intervals when light passingthrough said objective lens is incident on said first and secondphotoconductors and for disconnecting said memory means from said thirdresistor when light passing said objective lens is not incident on saidfirst and second photoconductors; and control means coupled to saidcapacitor memory means to control the open time of said shutter inaccordance with the stored voltage in said capacitor memory means.
 9. Ina camera having an objective lens and a shutter moveable between closedand open positions, an exposure control arrangement comprising: lightintensity to voltage conversion means for converting essentially eachvalue of the intensity of the light passing through said objective lensduring use of said camera to a corresponding voltage which isessentially linearly proportional to a logarithm of the value of saidiNtensity, said conversion means including a first photoconductor, asecond photoconductor series connected to said first photoconductor,said first and second photoconductors being arranged to receive saidlight passing through said objective lens, first and second seriesconnected resistance elements connected in parallel with said secondphotoconductor, and a potentiometer connected to the junction of saidseries connected resistance elements; capacitor memory means for storingsaid voltage; switch means for coupling said capacitor memory means tosaid potentiometer during intervals when light passing through saidobjective lens is incident on said first and second photoconductors andfor disconnecting said capacitor memory means from said potentiometerwhen light passing through said objective lens is not incident on saidfirst and second photoconductors; and control means coupled to saidcapacitor memory means to control the open time of said shutter inaccordance with the stored voltage on said capacitor memory means. 10.In a camera having an objective lens and a shutter moveable betweenclosed and open positions, an exposure control arrangement comprising:light intensity to voltage conversion means for converting essentiallyeach value of the intensity of the light passing through said objectivelens during use of said camera to a corresponding voltage which isessentially linearly proportional to a logarithm of the value of saidintensity, said conversion means including a first photoconductor, asecond photoconductor series connected to said first photoconductor,said first and second photoconductors being arranged to receive saidlight passing through said objective lens, first and second seriesconnected resistance elements connected in parallel with said secondphotoconductor, and a third resistance element connected to the junctionof said series connected resistance elements; amplifying circuit meansconnected to said junction for providing an output voltage proportionalto said voltage, capacitor memory means for storing said output voltage;switch means for coupling said capacitor memory means to said amplifyingmeans during intervals when light passing through said objective lens isincident on said first and second photoconductors and for disconnectingsaid capacitor memory means from said amplifying means when the lightpassing through said objective lens is not incident on said first andsecond photoconductors; and control means coupled to said capacitormemory means to control the open time of said shutter in accordance withthe stored voltage in said capacitor memory means.
 11. In a camerahaving an objective lens and a shutter moveable between closed and openpositions, an exposure control arrangement comprising: a photoconductorfor producing an output current related to the intensity of the lightpassing through said objective lens during use of said camera; a diodeseries connected with said photoconductor for producing a voltage whichis essentially linearly proportional to a logarithm of the value of theintensity of the light incident on said photoconductor, said seriesconnected diode and photoconductor being connected across a source ofoperating potential; capacitor memory means selectively coupled to thejunction of said photoconductor and said diode for storing at least aportion of said voltage; and control means for controlling the open timeof said shutter in accordance with the stored voltage in said capacitormemory means.
 12. In a camera, an exposure control arrangement as setforth in claim 11 further comprising: an amplifying stage coupling saidjunction to said capacitor memory means, said amplifying stage being inthe configuration of an emitter follower.
 13. In a camera, an exposurecontrol arrangement as set forth in claim 12, wherein said amplifyingstage comprises: a transistor having a control electrode and apotentiometer, having a tap, series connectEd across a source ofoperating potential, said control electrode of said transistor beingcoupled to said junction and the tap of said potentiometer beingconnected to said capacitor memory means.